Method of fabricating liquid crystal display device

ABSTRACT

The method of fabricating a liquid crystal display device includes the steps of (a) fabricating a switching device on a substrate, (b) forming an interlayer insulating film on the substrate such that the switching device is covered with the interlayer insulating film, and (c) forming a transparent electrode on the interlayer insulating film, the transparent electrode being electrically connected to the switching device through the interlayer insulating film, the step (c) including (c1) depositing electrically conductive, transparent and amorphous material on the interlayer insulating film, (c2) patterning the material into the transparent electrode, and (c3) turning the transparent electrode into polysilicon by thermal annealing carried out after formation of an alignment film.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a division of co-pending application Ser. No.10/692,736, filed on Oct. 27, 2003, the entire contents of which arehereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a method of fabricating a liquid crystaldisplay device, and more particularly to such a method including thestep of forming an electrically conductive transparent film in apredetermined pattern on an interlayer insulating film comprised of anelectrically insulating organic film.

2. Description of the Related Art

A liquid crystal display device is grouped into a light-transmissiontype one, a light-reflection type one and a combination type one independence on a light source.

A light-transmission type liquid crystal display device is designed toinclude a back-light device as a light source for displaying images. Alight-reflection type liquid crystal display device is designed toinclude a light-reflector, at which incident light is reflected towardsa viewer. Hence, a light-reflection type liquid crystal display deviceis not necessary to have a back-light device as a light source unlike alight-transmission type liquid crystal display device. A combinationtype liquid crystal display device is designed to have the samestructure as that of a light-transmission type liquid crystal displaydevice for a half of a display area and further have the same structureas that of a light-reflection type liquid crystal display device for therest of a display area.

Among the above-mentioned three type liquid crystal display devices, alight-transmission liquid crystal display device is usually designed toinclude a thin film transistor (TFT) or a metal-insulator-metal (MIM) asa switching device for driving and controlling a pixel electrode. Apixel electrode is usually comprised of an electrically conductivetransparent film such as an indium-tin oxide (ITO) film for ensuringhigh light-transmissivity and low resistance.

Many methods have been suggested for patterning indium-tin oxide (ITO)into a pixel electrode.

For instance, Japanese Patent Application Publication No. 6-88973 hassuggested a method of patterning ITO into a pixel electrode, includingthe steps of depositing indium-tin oxide on an inorganic interlayinsulating film by sputtering at 0 to 100 degrees centigrade, patterningthe deposited indium-tin oxide into a pixel electrode, and annealing thepixel electrode at 200 to 400 degrees centigrade, preferably at 230 to380 degrees centigrade, in hydrogen atmosphere. It is said in thePublication that annealing for reducing dangling bond in a semiconductorlayer of a thin film transistor and further for enhancing electricalcharacteristics and annealing for light-transmissivity of ITO andfurther for reducing electrical resistivity of ITO can be carried out assingle annealing.

Japanese Patent Application Publication No. 9-258247 has suggested amethod of patterning ITO into a pixel electrode on an electricallyinsulating organic film such as an acrylic resin film, including thesteps of depositing indium-tin oxide on an electrically insulatingorganic film composed of acrylic resin by sputtering at about 230degrees centigrade, annealing the indium-tin oxide immediately after thedeposition of the indium-tin oxide at a temperature equal to or greaterthan 100 degrees centigrade but equal to or smaller than a temperatureat which the indium-tin oxide was deposited, and patterning theindium-tin oxide into a pixel electrode. It is said in the Publicationthat it is possible to reduce a line-width shift in the step ofpatterning ITO by carrying out annealing after deposition of ITO.

If an interlayer insulating film comprised of an electrically insulatingorganic film is annealed at 230 degrees centigrade or higher assuggested in the above-mentioned Japanese Patent Application PublicationNo. 6-88973, the electrically insulating organic film would be usuallydecomposed, resulting in reduction in light-transmissivity. Hence,annealing for reducing dangling bond in a semiconductor layer of a thinfilm transistor and enhancing electric characteristics of the same isusually carried out prior to formation of an electrically insulatingorganic film independently of annealing to be carried out afterdeposition of indium-tin oxide.

Japanese Patent Application Publication No. 2001-343901 has suggested amethod of patterning indium-tin oxide both on an electrically insulatingorganic film such as an acrylic resin film and an electricallyinsulating inorganic film such as a SiN film. The suggested methodincludes the steps of depositing indium-tin oxide on both on anelectrically insulating organic film and an electrically insulatinginorganic film, annealing the indium-tin oxide at 150 to 220 degreescentigrade, preferably at 200 to 220 degrees centigrade, and patterningthe indium-tin oxide to a pixel electrode subsequently to the annealingstep.

Japanese Patent Application Publications Nos. 2001-345023 and2001-345024 suggest a method of patterning ITO into a pixel electrode,including the steps of depositing indium-tin oxide on an electricallyinsulating organic film, applying O₂, Ar or CF₄ plasma to the indium-tinoxide such that the indium-tin oxide has a crystal diameter in the rangeof 20 nm to 50 nm, and patterning the indium-tin oxide into a pixelelectrode. It is said in the Publications that by carrying out annealingafter patterning indium-tin oxide into a pixel electrode or applyingplasma to indium-tin oxide before patterning the indium-tin oxide into apixel electrode, indium-tin oxide deposited on an electricallyinsulating organic film and indium-tin oxide deposited on anelectrically insulating inorganic film would have etching rates almostequal to each other, resulting in that a line-width shift can be reducedin the step of patterning ITO into a pixel electrode. It is further saidin Japanese Patent Application Publication No. 2001-345023 that theindium-tin oxide may be annealed at 150 to 220 degrees centigrade afterthe step of patterning the indium-tin oxide into a pixel electrode.

Japanese Patent Application Publication No. 10-161158 has suggested amethod of patterning indium-tin oxide into a pixel electrode on anelectrically insulating organic film such as a poly-imide resin film oran acrylic resin film. The suggested method includes the step ofroughing a surface of an electrically insulating organic film bysputtering etching, dry etching or irradiation of ultra-violet raysbefore carrying out a step of patterning ITO into a pixel electrode. Bycarrying out the step of roughing the surface, ITO and the electricallyinsulating organic film would make contact with each other through alarge area, which ensures close contact between ITO and the electricallyinsulating organic film. As a result, it would be possible to accuratelypattern ITO into a pixel electrode. The step of roughing the surface maybe carried out prior to or subsequently to formation of a contact hole.

If indium-tin oxide is patterned into a pixel electrode on anelectrically insulating organic film such as a acrylic resin film inaccordance with the method suggested in Japanese Patent ApplicationPublication No. 6-88973, the electrically insulating organic film wouldbe decomposed, resulting in that the resultant pixel electrode would becolored, and hence, light-transmissivity would be reduced, because atemperature at which the indium-tin oxide is annealed is usually higherthan a temperature at which an electrically insulating organic film isnot decomposed. If an electrically insulating organic film is annealedat 200 to 300 degrees centigrade, it would be possible to prevent theelectrically insulating organic film from being decomposed, but a rangeof 200 to 300 degrees centigrade is too low to reduce dangling bond in asemiconductor layer of a thin film transistor. Accordingly, it isimpossible to design the method to include only one annealing step.

In accordance with the method suggested in Japanese Patent ApplicationPublication No. 9-258247, an indium-tin oxide film is reformed by gasdischarged from an electrically insulating organic film duringpatterning indium-tin oxide into a pixel electrode, resulting etchingresidue in the step of patterning indium-tin oxide into a pixelelectrode. If indium-tin oxide is deposited at 100 degrees centigrade orlower, such etching residue can be suppressed to some degree, but it isnot possible to completely suppress such etching residue. Since themethod includes a step of carrying out annealing after deposition ofindium-tin oxide, the method unavoidably carries out an annealing steptwice.

In the methods suggested in the above-mentioned Japanese PatentApplication Publications Nos. 2001-345023 and 345024, plasma is appliedto indium-tin oxide before patterning the indium-tin oxide into a pixelelectrode, namely, after formation of a contact hole throughout theelectrically insulating organic film. According to the experimentshaving been conducted by the inventors, it was found out that contactresistance between the indium-tin oxide and an underlying metal film wasincreased in dependence on gas used for generating plasma. Inparticular, such contact resistance is significantly increased whenfluorine-containing gas such as CF₄ or helium (He) gas is used forgenerating plasma.

In the method suggested in the above-mentioned Japanese PatentApplication Publication No. 10-161158, if ultra-violet rays are firstirradiated to the electrically insulating organic film, the electricallyinsulating organic film would be decomposed, resulting in that theresultant pixel electrode would be colored.

In addition, if sputter etching or dry etching is to be carried outprior to formation of a contact hole, it would be possible to do soafter baking an electrically insulating organic film, only if theelectrically insulating organic film is not photo-sensitive. Incontrast, if the electrically insulating organic film isphoto-sensitive, it would be necessary to carry out sputter etching ordry etching after the electrically insulating organic film was formed.By carrying out sputter etching or dry etching in a condition in whichthe electrically insulating organic film has been already formed, anetching apparatus might be contaminated with the result of significantreduction in productivity, and a roughened surface of the electricallyinsulating organic film would be planarized during baking theelectrically insulating organic film.

If sputter etching or dry etching is carried out after formation of acontact hole, there is caused a problem that the above-mentioned contactresistance is increased.

Increase in a contact resistance might cause horizontal cross-talkand/or non-uniformity of horizontal lines in a common-storage typetwisted nematic liquid crystal display device or an in-plane switchingtype liquid crystal display device. Specifically, it is necessary in acommon-storage type twisted nematic liquid crystal display device tobind common lines to one another for applying a common voltage to thecommon lines. However, if a thin film transistor is designed to have astructure in which common lines are bound to one another through anindium-tin oxide film formed on an interlayer insulating film, a contactresistance would be increased due to an electrically insulating organicfilm, and hence, the common lines would unavoidably have a highresistance.

Recently, an in-plane switching type liquid crystal display device iscommercially available. An in-plane switching type liquid crystaldisplay device includes a common electrode comprised of an electricallyconductive transparent film and formed on an electrically insulatingorganic interlayer film above a signal line, and a pixel electrodecomprised of the electrically conductive transparent film of which thecommon electrode is comprised, and formed in facing relation to thecommon electrode. Such an in-plane switching type liquid crystal displaydevice has a high aperture ratio. For instance, an in-plane switchingtype liquid crystal display device is suggested in WO98/47044.

It is quite important for an in-plane switching type liquid crystaldisplay device to accurately pattern an electrically conductivetransparent film formed on an electrically insulating organic film, intoa pixel electrode uniformly within a substrate. If process control for astep of patterning an electrically conductive transparent film into apixel electrode is insufficient, there would be resulted innon-uniformity in displayed images. In addition, it is important for acommon storage type in-plane switching type liquid crystal displaydevice to reduce a contact resistance between an electrically conductivetransparent film and an underlying metal film.

Thus, there is a need for a method of fabricating a liquid crystaldisplay device which method is capable of enhancing accuracy with whichan electrically conductive transparent film formed on an electricallyinsulating organic interlayer film is patterned into a pixel electrode,and accomplishing a low contact resistance between the electricallyconductive transparent film and an underlying metal film.

Japanese Patent Application Publication No. 9-246210 has suggested amethod of patterning an electrically conductive transparent film,including the steps of forming an electrically conductive transparentfilm on an organic or inorganic substrate or film, forming a mask on theelectrically conductive transparent film in a predetermined pattern,implanting hydrogen ions into the electrically conductive transparentfilm through the mask, and etching for removal portions of theelectrically conductive transparent film into which the hydrogen ionswere implanted.

Japanese Patent Application Publication No. 9-293875 has suggested amethod of fabricating a semiconductor device, including the steps offorming a light-permeable film on a monocrystal semiconductor substrate,fabricating a non-monocrystal semiconductor device on thelight-permeable film, fabricating a monocrystal semiconductor device onthe monocrystal semiconductor substrate, forming an electricallyconductive amorphous film on the monocrystal semiconductor substrate,and re-crystallizing the electrically conductive amorphous film to makethe film transparent.

Japanese Patent Application Publication No. 11-95239 has suggested amethod of fabricating a liquid crystal display device, including thestep of forming an indium-tin oxide film on an electrically insulatingsubstrate by sputtering in which there is used water vapor having apartial pressure in the range of 0.002 Pa to 0.010 Pa.

Japanese Patent Application Publication No. 2002-296609 has suggested amethod of fabricating a liquid crystal display device including a buswire arranged on a substrate in a matrix, a switching deviceelectrically connected to the bus wire, and a pixel electrodeelectrically connected to the bus wire with an interlayer insulatingfilm being sandwiched therebetween the method including the step ofkeeping the substrate at 100 to 170 degrees centigrade while anelectrically conductive transparent film is formed on the interlayerinsulating film.

SUMMARY OF THE INVENTION

In view of the above-mentioned problems in the conventional methods, itis an object of the present invention to provide a method of fabricatinga liquid crystal display device which method is capable of forming acontact hole throughout an electrically insulating organic or inorganicinterlayer film and accurately patterning an electrically conductivetransparent film into a pixel electrode uniformly within a substratewithout etching residue of the electrically conductive transparent film,and further of preventing a contact resistance between the electricallyconductive transparent film and an underlying metal film fromincreasing, ensuring no poor quality in displayed images.

In one aspect of the present invention, there is provided a method offabricating a liquid crystal display device, including the steps of (a)fabricating a switching device on a substrate, (b) forming an interlayerinsulating film on the substrate such that the switching device iscovered with the interlayer insulating film, and (c) forming atransparent electrode on the interlayer insulating film, the transparentelectrode being electrically connected to the switching device throughthe interlayer insulating film, the step (c) including (c1) depositingelectrically conductive, transparent and amorphous material on theinterlayer insulating film, (c2) patterning the material into thetransparent electrode, and (c3) turning the transparent electrode intopolysilicon by thermal annealing carried out after formation of analignment film.

For instance, the step (b) may include the steps of (b1) forming anelectrically insulating inorganic film on the substrate such that theswitching device is covered with the electrically insulating inorganicfilm, and (b2) forming an electrically insulating organic film on theelectrically insulating inorganic film.

It is preferable that the electrically insulating organic film is formedcovering therewith at least partially at least a signal line including adrain electrode of the switching device, in the step (b2).

For instance, the step (a) may include the steps of (a1) forming both ascanning line including a gate electrode of the switching device and acommon line through which a common voltage is applied, on the substrate,(a2) forming a gate insulating film on the substrate such that thescanning line and the common line are covered with the gate insulatingfilm, (a3) forming a semiconductor layer on the gate insulating film,the semiconductor layer acting as an active layer of the switchingdevice, and (a4) forming both a signal line including a drain electrodeof the switching device and a source electrode of the switching device,the signal line intersecting with the scanning line, and the step (c)may include the step of patterning the electrically conductive,transparent and amorphous material into a pixel electrode and a commonelectrode on the interlayer insulating film, the pixel electrode beingin electrical connection with the switching device, the common electrodebeing in electrical connection with the common line.

It is preferable that the material is indium-tin oxide (ITO).

It is preferable that the material is deposited on the interlayerinsulating film in the step (c1) at room temperature (RM).

It is preferable that the material is deposited on the interlayerinsulating film in the step (c1) in atmosphere including at leastmoisture or hydrogen.

It is preferable that the thermal annealing is carried out in the step(c3) in the range of 180 to 240 degrees centigrade both inclusive.

There is further provided a method of fabricating a liquid crystaldisplay device, including the steps of (a) fabricating a switchingdevice on a substrate, (b) forming an interlayer insulating film on thesubstrate such that the switching device is covered with the interlayerinsulating film, the interlayer insulating film being comprised of anelectrically insulating inorganic film and an electrically insulatingorganic film formed on the electrically insulating inorganic film, and(c) forming a transparent electrode on the interlayer insulating film,the transparent electrode being electrically connected to the switchingdevice through the interlayer insulating film, the step (c) including(c1) patterning the electrically insulating organic film, (c2) applyingplasma to the substrate including the electrically insulating organicfilm, (c3) forming a contact hole throughout the electrically insulatinginorganic film, (c4) depositing electrically conductive transparentmaterial on the interlayer insulating film, and (c5) patterning thematerial into the transparent electrode.

It is preferable that the electrically insulating organic film is formedcovering therewith at least partially at least a signal line including adrain electrode of the switching device, in the step (c1).

For instance, the step (a) may include the steps of (a1) forming both ascanning line including a gate electrode of the switching device and acommon line through which a common voltage is applied, on the substrate,(a2) forming a gate insulating film on the substrate such that thescanning line and the common line are covered with the gate insulatingfilm, (a3) forming a semiconductor layer on the gate insulating film,the semiconductor layer acting as an active layer of the switchingdevice, and (a4) forming both a signal line including a drain electrodeof the switching device and a source electrode of the switching device,the signal line intersecting with the scanning line, and the step (c5)may include the step of patterning the electrically conductivetransparent material into a pixel electrode and a common electrode onthe interlayer insulating film, the pixel electrode being in electricalconnection with the switching device, the common electrode being inelectrical connection with the common line.

It is preferable that the plasma is helium (He) plasma.

For instance, the step (c3) may include (c3-1) forming a photoresist onthe interlayer insulating film in a predetermined pattern, (c3-2)post-baking the photoresist, and (c3-3) etching the electricallyinsulating inorganic film with the photoresist being used as a mask bywet-etching or both wet- and dry-etching.

It is preferable that the electrically conductive transparent materialis indium-tin oxide (ITO) or indium-zinc oxide (IZO).

There is still further provided a method of fabricating a liquid crystaldisplay device, including the steps of (a) fabricating a switchingdevice on a substrate, (b) forming an interlayer insulating film on thesubstrate such that the switching device is covered with the interlayerinsulating film, the interlayer insulating film being comprised of anelectrically insulating inorganic film and an electrically insulatingorganic film formed on the electrically insulating inorganic film, and(c) forming a transparent electrode on the interlayer insulating film,the transparent electrode being electrically connected to the switchingdevice through the interlayer insulating film, the step (c) including(c1) patterning the electrically insulating organic film, (c2) forming acontact hole throughout the electrically insulating inorganic film, (c3)depositing electrically conductive transparent material on theinterlayer insulating film, and (c4) patterning the material into thetransparent electrode, the step (c2) including (c2-1) forming aphotoresist on the interlayer insulating film in a predeterminedpattern, and (c2-2) applying dry-etching to the electrically insulatinginorganic film with the photoresist being used as a mask withoutpost-baking the photoresist.

It is preferable that the electrically insulating organic film is formedcovering therewith at least partially at least a signal line including adrain electrode of the switching device, in the step (c1).

For instance, the step (a) may include the steps of (a1) forming both ascanning line including a gate electrode of the switching device and acommon line through which a common voltage is applied, on the substrate,(a2) forming a gate insulating film on the substrate such that thescanning line and the common line are covered with the gate insulatingfilm, (a3) forming a semiconductor layer on the gate insulating film,the semiconductor layer acting as an active layer of the switchingdevice, and (a4) forming both a signal line including a drain electrodeof the switching device and a source electrode of the switching device,the signal line intersecting with the scanning line, and the step (c5)including the step of patterning the electrically conductive transparentmaterial into a pixel electrode and a common electrode on the interlayerinsulating film, the pixel electrode being in electrical connection withthe switching device, the common electrode being in electricalconnection with the common line.

It is preferable that the electrically conductive transparent materialis indium-tin oxide (ITO) or indium-zinc oxide (IZO).

The advantages obtained by the aforementioned present invention will bedescribed hereinbelow.

In accordance with the present invention, an amorphous indium-tin oxidefilm is formed on an interlayer insulating film in a predeterminedpattern, and then, the amorphous indium-tin oxide film ispoly-crystallized by thermal annealing carried out after formation of analignment film. Thus, the present invention makes it possible to patternan indium-tin oxide film to a pixel electrode with accuracy anduniformity, but without etching residue. In particular, the presentinvention makes it possible, in an in-plane switching type liquidcrystal display device including a common electrode and a pixelelectrode both comprised of an indium-tin oxide film on an interlayerinsulating film, to prevent non-uniformity in displayed images, causedby non-uniformity in patterning the indium-tin oxide film, and furtherto enhance a fabrication yield.

In addition, the present invention makes it possible to reduce anannealing step by one.

The present invention makes it possible, in a liquid crystal displaydevice including an interlayer insulating film comprised of anelectrically insulating organic film and an electrically insulatinginorganic film and formed on a thin film transistor, to accurately anduniformly pattern an electrically conductive transparent film, andprevent a contact resistance between the electrically conductivetransparent film and an underlying metal film, by applying helium (He)plasma to an interlayer insulating film prior to formation of a contacthole throughout the electrically insulating inorganic film. Inparticular, the present invention makes it possible, in an in-planeswitching type liquid crystal display device including a commonelectrode and a pixel electrode both comprised of an electricallyconductive transparent film on an interlayer insulating film, to preventnon-uniformity in displayed images, caused by non-uniformity inpatterning the electrically conductive transparent film or by anincreased contact resistance, and further to enhance a fabricationyield.

The above and other objects and advantageous features of the presentinvention will be made apparent from the following description made withreference to the accompanying drawings, in which like referencecharacters designate the same or similar parts throughout the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a substrate on which a thin film transistor isto be fabricated, in an in-plane switching type liquid crystal displaydevice fabricated by a method in accordance with the first embodiment ofthe present invention.

FIG. 2 is an enlarged plan view of a pixel in the substrate illustratedin FIG. 1.

FIG. 3A is a cross-sectional view taken along the line 3A-3A in FIG. 2.

FIG. 3B is a cross-sectional view taken along the line 3B-3B in FIG. 2.

FIG. 3C is a cross-sectional view taken along the line 3C-3C in FIG. 2.

FIG. 4 is a plan view of a pixel, illustrating a first step of a methodof fabricating a liquid crystal display panel including the substrateillustrated in FIG. 1.

FIG. 5A is a cross-sectional view taken along the line 5A-5A in FIG. 4.

FIG. 5B is a cross-sectional view taken along the line 5B-5B in FIG. 4.

FIG. 5C is a cross-sectional view taken along the line 5C-5C in FIG. 4.

FIG. 6 is a plan view of a pixel, illustrating a second step of a methodof fabricating a liquid crystal display panel including the substrateillustrated in FIG. 1.

FIG. 7A is a cross-sectional view taken along the line 7A-7A in FIG. 6.

FIG. 7B is a cross-sectional view taken along the line 7B-7B in FIG. 6.

FIG. 7C is a cross-sectional view taken along the line 7C-7C in FIG. 6.

FIG. 8 is a plan view of a pixel, illustrating a third step of a methodof fabricating a liquid crystal display panel including the substrateillustrated in FIG. 1.

FIG. 9A is a cross-sectional view taken along the line 9A-9A in FIG. 8.

FIG. 9B is a cross-sectional view taken along the line 9B-9B in FIG. 8.

FIG. 9C is a cross-sectional view taken along the line 9C-9C in FIG. 8.

FIG. 10 is a plan view of a pixel, illustrating a fourth step of amethod of fabricating a liquid crystal display panel including thesubstrate illustrated in FIG. 1.

FIG. 11A is a cross-sectional view taken along the line 11A-11A in FIG.10.

FIG. 11B is a cross-sectional view taken along the line 11B-11B in FIG.10.

FIG. 11C is a cross-sectional view taken along the line 11C-11C in FIG.10.

FIG. 12 is a plan view of a pixel, illustrating a fifth step of a methodof fabricating a liquid crystal display panel including the substrateillustrated in FIG. 1.

FIG. 13A is a cross-sectional view taken along the line 13A-13A in FIG.12.

FIG. 13B is a cross-sectional view taken along the line 13B-13B in FIG.12.

FIG. 13C is a cross-sectional view taken along the line 13C-13C in FIG.12.

FIG. 14 is a plan view of terminal sections around the substrateillustrated in FIG. 1.

FIG. 15A is a cross-sectional view taken along the line 15A-15A in FIG.14.

FIG. 15B is a cross-sectional view taken along the line 15B-15B in FIG.14.

FIG. 16 is a cross-sectional view of a pixel in a liquid crystal displaypanel including the substrate illustrated in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments in accordance with the present invention will beexplained hereinbelow with reference to drawings.

First Embodiment

FIG. 1 is a plan view of a substrate on which a thin film transistor(TFT) is to be fabricated, in a liquid crystal display device fabricatedby a method in accordance with the first embodiment of the presentinvention. In the first embodiment, an in-plane switching type liquidcrystal display device is fabricated. Hereinbelow, the substrate isreferred to simply as a TFT substrate.

As illustrated in FIG. 1, the TFT substrate 10 includes, on a surfacethereof facing an opposing substrate, a plurality of scanning lines 11,a plurality of signal lines 12 each extending perpendicularly to thescanning lines 11, and a plurality of common lines 13 each extendingbetween adjacent scanning lines 11 in parallel with the scanning lines11. Thin film transistors (TFTs) 14 are fabricated in a matrix atintersections of the scanning lines 11 with the signal lines 12.

Each of the scanning lines 11 is connected at an end thereof to ascanning line terminal 15. A drive signal is input to each of thescanning lines 11 through each of the scanning line terminals 15 from anexternal driver circuit (not illustrated). Each of the signal lines 12is connected at an end thereof to a signal-line terminal 16. A drivesignal is input to each of the signal lines 12 through each of thesignal-line terminals 16 from an external driver circuit (notillustrated).

The common lines 13 are bound to one another in order to apply a commonvoltage as a reference voltage for driving liquid crystal thereto.Specifically, common-line binding lines 17 a and 17 b extend at oppositemarginal areas of the TFT substrate 10 in parallel with the signal lines12. The common-line binding line 17 a connects one ends (for instance,left ends) of the common lines 13 to one another, and the common-linebinding line 17 b connects the other ends (for instance, right ends) ofthe common lines 13 to one another. The common lines 13 and pixelelectrodes electrically connected to source electrodes of TFTs 14cooperate with each other to define capacities therebetween. Thecommon-line binding line 17 a is connected at ends thereof to acommon-line terminal 18 a, and the common-line binding line 17 b isconnected at ends thereof to a common-line terminal 18 b.

FIG. 2 is an enlarged plan view of a pixel in the TFT substrate 10illustrated in FIG. 1. FIGS. 3A, 3B and 3C are cross-sectional viewstaken along the lines 3A-3A, 3B-3B and 3C-3C in FIG. 2, respectively.

As illustrated in FIG. 2, a pair of the scanning lines 11 adjacent toeach other and a pair of the signal lines 12 adjacent to each otherintersect with each other. Each of pixels has a display area defined asan area surrounded by a pair of the scanning lines 11 and a pair of thesignal lines 12. Each of pixels has a comb-shaped pixel electrode 21 anda comb-shaped common electrode 22. Teeth of the pixel electrode 21 andteeth of the common electrode 22 are alternately arranged and face eachother. An electric field is generated in parallel with the TFT substrate10 between the pixel electrode 21 and the common electrode 22 forcontrolling alignment of liquid crystal molecules.

As illustrated in FIG. 3, the TFT substrate 10 is comprised of anelectrically insulating transparent substrate 20 such as a glasssubstrate, the above-mentioned scanning lines 11 and common lines 13both formed on the electrically insulating transparent substrate 20, agate insulating film 31 formed on the substrate 20 such that thescanning and common lines 11 and 13 are covered with the gate insulatingfilm 31, a thin film transistor (TFT) 14 fabricated on the gateinsulating film 31, a passivation film 32 formed on the gate insulatingfilm 31 such that the thin film transistor 14 is covered with thepassivation film 32, an electrically insulating organic film 33 formedon the passivation film 32, and the above-mentioned pixel and commonelectrodes 21 and 22 both formed on the electrically insulating organicfilm 33.

The passivation film 32 and the electrically insulating organic film 33constitute an interlayer insulating film 38. The pixel and commonelectrodes 21 and 22 are formed on the interlayer insulating film 38, asillustrated in FIGS. 3A and 3C.

The thin film transistor 14 is comprised of a gate electrode 23 formedon the electrically insulating transparent substrate 20, theabove-mentioned gate insulating film 31 covering the gate electrode 23therewith, a source electrode 24 formed on the gate insulating film 31,a drain electrode 25 formed on the gate insulating film 31, and asemiconductor layer 34 formed on the gate insulating film 31 between thesource and drain electrodes 24 and 25.

In the first embodiment, the thin film transistor 14 is comprised of areverse-stagger type TFT. As illustrated in FIG. 2, the gate electrodeof the thin film transistor 14 is formed as a part of the scanning line11, and the drain electrode of the thin film transistor 14 is formed asa part of the signal line 12.

As illustrated in FIG. 3A, the pixel electrode 21 is electricallyconnected to the source electrode 24 of the thin film transistor 14through a contact hole 26 formed throughout the interlayer insulatingfilm 38. As illustrated in FIG. 3C, the common electrode 22 iselectrically connected to the common line 13 through a contact hole 37formed throughout the interlayer insulating film 38 and the gateinsulating film 31.

The thin film transistor 14 receives a scanning signal through thescanning line 11 and the gate electrode 23, and further receives adisplay signal through the signal line 12 and the drain electrode 25 forwriting electric charges into the pixel electrode 21.

As illustrated in FIGS. 3A and 3C, an accumulation capacitor is formedbetween the common line 13 and an accumulation capacity electrode 35.

Hereinbelow is explained a method of fabricating the thin filmtransistor 14 in the first embodiment.

FIGS. 4, 6, 8, 10, 12 and 2 are plan views of each of steps forfabrication of a pixel. FIGS. 5A, 7A, 9A, 11A, 13A and 3A arecross-sectional views taken along the lines XA-XA (X=4, 6, 8, 10, 12 and2) in FIGS. 4, 6, 8, 10, 12 and 2

Similarly, FIGS. 5B, 7B, 9B, 11B, 13B and 3B are cross-sectional viewstaken along the lines XB-XB (X=4, 6, 8, 10, 12 and 2) in FIGS. 4, 6, 8,10, 12 and 2, and FIGS. 5C, 7C, 9C, 11C, 13C and 3C are cross-sectionalviews taken along the lines XC-XC (X=4, 6, 8, 10, 12 and 2) in FIGS. 4,6, 8, 10, 12 and 2. FIGS. 5A, 7A, 9A, 11A, 13A and 3A illustratecross-sections of the thin film transistor 14, the contact hole 26 forthe pixel electrode 21, and the accumulation capacity. FIGS. 5B, 7B, 9B,11B, 13B and 3B illustrate cross-sections of the pixel. FIGS. 5C, 7C,9C, 11C, 13C and 3C illustrate cross-sections of the signal line 12, thecontact hole 27 for the common electrode 22, and the accumulationcapacity.

As illustrated in FIGS. 4 and 5A to 5C, an electrically conductive layeris formed on the substrate 20 by sputtering by a thickness in the rangeof about 100 to 300 nanometers. The electrically conductive layer iscomprised of a chromium (Cr) layer, a molybdenum (Mo) layer, a Cr/Allayer or a Mo/Al layer, for instance. Then, the electrically conductivelayer is etched by photolithography into the scanning line 11 includingthe gate electrode 23, the common line 13, the scanning-line terminal 16(not illustrated), and the common-line terminals 18 a and 18 b (notillustrated).

Then, as illustrated in FIGS. 6 and 7A to 7C, the gate insulating film31 comprised of a silicon nitride film is formed on the substrate 20 byplasma-enhanced chemical vapor deposition (PCVD) by a thickness in therange about 300 to 500 nanometers such that the scanning line 11, thecommon line 13, the scanning-line terminal 15 (not illustrated) and thecommon-line terminals 18 a and 18 b (not illustrated) are covered withthe gate insulating film 31.

Then, an amorphous silicon (a-Si) film is formed on the gate insulatingfilm 31 by a thickness in the range of about 150 to 300 nanometers, andthen, an amorphous silicon film (n+a-Si) into which phosphorus (P) wasdoped is formed on the amorphous silicon (a-Si) film by a thickness inthe range of about 30 to 50 nanometers. Then, these amorphous siliconfilms (a-Si and n+a-Si) are etched by photolithography into thesemiconductor layer 34 on the gate insulating film 31. The semiconductorlayer 34 acts as an active layer of the thin film transistor 14.

Concurrently with the formation of the semiconductor layer 34, asemiconductor layer 64 is formed on the gate insulating film 31 atintersections of the scanning line 11 and the common line 13 with thesignal line 12 for enhancing withstand voltages of the scanning line 11,the common line 13 and the signal line 12.

Then, as illustrated in FIGS. 8 and 9A to 9C, an electrically conductivelayer is formed on the gate insulating film 31 by sputtering by athickness in the range of about 100 to 400 nanometers. For instance, theelectrically conductive layer is comprised of a chromium (Cr) layer, amolybdenum (Mo) layer, a Cr/Al/Cr layer or a Mo/Al/Mo layer. Then, theelectrically conductive layer is etched by photolithography into thesource electrode 24, the drain electrode 25, the accumulation capacityelectrode 35, the signal line 12 and the signal-line terminal 16.

Then, the n+a-Si layer of the semiconductor layer 34 is etched into achannel with the source and drain electrodes 24 and 25 being used as amask.

As illustrated in FIGS. 10 and 11, the passivation film 32 is formed onthe gate insulating film 31 by plasma-enhanced chemical vapor deposition(PCVD) by a thickness in the range of about 100 to 300 nanometers suchthat the source electrode 24, the drain electrode 25, the semiconductorlayer 34, the accumulation capacity electrode 35, the signal line 12 andthe signal-line terminal 16 are covered with the passivation film 32.The passivation film 32 is comprised of an inorganic film such as asilicon nitride film.

Then, the resultant is annealed at about 280 degrees centigrade innitrogen atmosphere.

Then, the electrically insulating organic film 33 is formed on thepassivation film 32 by a thickness in the range of about 1.5 to 3.5micrometers through the use of a positive photo-sensitive novolakresist. Then, as illustrated in FIGS. 11A and 11C, holes 66 and 67through which the contact holes 26 and 27 will be formed later areformed throughout the electrically insulating organic film 33 byphotolithography and etching. Then, the electrically insulating organicfilm 33 is baked at about 230 degrees centigrade.

Then, as illustrated in FIGS. 12 and 13A to 13C, the passivation film 32is etched by photolithography to thereby form the contact hole 26 (seeFIG. 13A) in alignment with the hole 66, through which the sourceelectrode 24 is exposed, and a contact hole (not illustrated) throughwhich a metal film of the signal-line terminal 16 is exposed.Concurrently, the passivation film 32 and the gate insulating film 31are etched to form the contact hole 27 (see FIG. 13C) in alignment withthe hole 67, through which the common line 13 is exposed, a contact hole(not illustrated) through which a metal film of the scanning-lineterminal 15 and a metal film of the common-line terminals 18 a and 18 bare exposed, and a contact hole (not illustrated) through which ends ofthe common lines 13 are exposed.

The passivation film 32 and the gate insulating film 31 may be etched bydry etching, wet etching or dry and wet etching.

Then, as illustrated in FIGS. 2 and 3A to 3C, an electrically conductivetransparent film comprised of an indium-tin oxide (ITO) film is formedon the electrically insulating organic film 33 by sputtering. Then, theelectrically conductive transparent film is etched by photolithographyinto the pixel electrode 21, the common electrode 22, a metal film ofthe scanning-line terminal 15, a metal film of the signal-line terminal16, a connection electrode (not illustrated) located on a metal film ofthe common-line terminals 18 a and 18 b, and the common-line bindinglines 17 a and 17 b such that, as illustrated in FIG. 3B, a commonelectrode 72 among the common electrodes 22 is formed on theelectrically insulating organic film 33 in alignment with the signalline 12, and a pixel electrode 71 among the pixel electrodes 21 isformed on the electrically insulating organic film 33 in alignment withthe accumulation capacity electrode 35. Thus, the pixel electrode 21 iselectrically connected to the source electrode 24 through the contacthole 26, the common electrode 22 is electrically connected to the commonline 13 through the contact hole 27, the connection electrode iselectrically connected to the metal film of the scanning-line terminal15, the metal film of the signal-line terminal 16 and the metal film ofthe common-line terminals 18 a and 18 b through the associated contactholes, and the common-line binding lines 17 a and 17 b are electricallyconnected to ends of the common lines 13 through the contact hole formedfor the common-line binding lines 17 a and 17 b. Structures of theterminals are explained later.

The indium-tin oxide film is deposited by reactive sputtering in argon(Ar) and oxygen (O₂) gases atmosphere. Oxygen gas is mixed with argongas at about 1 to 5 atom %. Water or hydrogen gas may be mixed to argongas at about 1 atom %. The substrate is not heated during deposition ofthe indium-tin oxide film, and the indium-tin oxide film is not annealedafter the deposition thereof. Thus, an amorphous indium-tin oxide filmis formed on the electrically insulating organic film 33.

The amorphous indium-tin oxide film is etched by wet etching through theuse of etchant such as aqua regia or oxalic acid. The amorphousindium-tin oxide film can be etched without etching residue, if a smallamount of water or hydrogen is added to etchant. A period of time duringwhich the amorphous indium-tin oxide film is etched is determined inaccordance with an etching rate of the film. It is possible to controlside-etching to be within about 1 micrometer on the electricallyinsulating organic film. Herein, side-etching is defined as a line widthobtained by subtracting a line width of an etched indium-tin oxide filmfrom a line width of a developed photoresist.

Hereinbelow is explained the terminals of the TFT substrate 10 in thefirst embodiment.

FIG. 14 is a plan view of the terminals of the TFT substrate 10. FIG.15A is a cross-sectional view taken along the line 15A-15A in FIG. 14,illustrating the scanning-line terminal 15 and the common-line terminals18 a and 18 b, and FIG. 15B is a cross-sectional view taken along theline 15B-15B in FIG. 14, illustrating the signal-line terminal 16.

As illustrated in FIG. 15A, the scanning-line terminal 15 and thecommon-line terminals 18 a and 18 b are formed as a connection electrode42 comprised of an electrically conductive transparent film (anindium-tin oxide film) of which the common electrode 22 is comprised,above a terminal metal film 41 formed on the electrically insulatingtransparent substrate 20 and comprised of a metal film of which thescanning line 11 is comprised.

As illustrated in FIG. 15B, the signal-line terminal 16 is formed as aconnection electrode 82 comprised of an electrically conductivetransparent film (an indium-tin oxide film) of which the commonelectrode 22 is comprised, above a terminal metal film 81 formed on thegate insulating film 31 and comprised of a metal film of which thesignal line 12 is comprised.

The connection electrode 42 is electrically connected to a terminalmetal film 41 through a contact hole 43 formed throughout the gateinsulating film 31 and the passivation film 32, and the connectionelectrode 82 is electrically connected to a terminal metal film 81through a contact hole 83 formed throughout the passivation film 32. Thescanning-line and signal-line terminals 15 and 16, namely, theconnection electrodes 42 and 82 are designed not to include theelectrically insulating organic film 33.

Side-etching of the indium-tin oxide film formed on the passivation film32 is smaller than side-etching of the indium-tin oxide film formed onthe electrically insulating organic film 33. Accordingly, since theside-etching of the indium-tin oxide film formed on the electricallyinsulating organic film 33 is controlled to be within about 1micrometer, no problems are caused.

The common lines 13 are electrically connected to the common-linebinding lines 17 a and 17 b through a contact hole 44 (see FIG. 14).Though not illustrated, the contact hole 44 has the same cross-sectionas that of the contact hole 43 illustrated in FIG. 15A.

In the first embodiment, each of the common-line binding lines 17 a and17 b are comprised of an electrically conductive transparent film. As analternative, the common-line binding lines 17 a and 17 b may becomprised of a metal film of which the signal line 12 is comprised.

Though not illustrated, the common-line binding lines 17 a and 17 b maybe electrically connected at a part thereof to an electricallyconductive transparent film formed on the electrically insulatingorganic film 33, through a contact hole formed throughout thepassivation film 32 and the electrically insulating organic film 33. Inaddition, the common-line binding lines 17 a and 17 b may beelectrically connected at ends thereof to the above-mentionedelectrically conductive transparent film formed on the electricallyinsulating organic film 33, through a contact hole formed throughout thegate insulating film 31 and the passivation film 32. The common-linebinding lines 17 a and 17 b may be electrically connected to the commonlines 13 through an electrically conductive transparent film in theabove-mentioned way. By electrically connecting the common-line bindinglines 17 a and 17 b to the common lines 13, it would be possible tolower a resistance of the common-line binding lines 17 a and 17 b.

Hereinbelow is explained a method of fabricating a liquid crystal panelincluding the above-mentioned TFT substrate 10.

FIG. 16 is a cross-sectional view of a pixel in the liquid crystalpanel.

The illustrated liquid crystal panel is comprised of the above-mentionedTFT substrate 10, an opposing substrate 50 arranged in facing relationto the TFT substrate 10, and a liquid crystal layer 55 sandwichedbetween the TFT substrate 10 and the opposing substrate 50.

The opposing substrate 50 is comprised of an electrically insulatingtransparent substrate 30 such as a glass substrate, a black matrix 52formed on a surface of the substrate 30 which surface faces the opposingsubstrate 50, three-colored color filters 53R, 53G and 53B formed on thesubstrate 30, covering the black matrix 52 therewith, an overcoat film54 formed on the color filters 53R, 53G and 53B, and an electricallyconductive transparent layer 56 formed on a surface of the substrate 30which surface faces oppositely to the TFT substrate 10.

The liquid crystal panel is fabricated as follows.

After fabricating the TFT substrate 10 in the above-mentioned way, analignment film 51 is formed on the electrically insulating organic film33. The alignment film 51 is compound polyimide alignment material, andhas a thickness in the range of 30 to 60 nanometers. Then, the TFTsubstrate 10 is baked at 180 to 240 degrees centigrade for aligning thealignment film 51.

Then, sealing material (not illustrated) composed of epoxy resinadhesive is adhered to a marginal area of the TFT substrate 10.

By baking the TFT substrate 10 after formation of the alignment film 51,the electrically conductive transparent film is also annealed. That is,by baking the TFT substrate 10 after formation of the alignment film 51,it is possible to turn the amorphous indium-tin oxide film into apoly-crystal indium-tin oxide film, enhance light-transmissivity of aresultant indium-tin oxide film, and reduce a resistance of a resultantindium-tin oxide film.

Then, an electrically conductive transparent layer 56 is formed on asurface of the substrate 30 which surface does not face the TFTsubstrate 10. The electrically conductive transparent layer 56 iscomprised of an indium-tin oxide film, for instance, and has a thicknessin the range of about 80 to 150 nanometers.

Then, the black matrix 52 is formed on a surface of the electricallyinsulating organic film 33 which surface faces the TFT substrate 10. Theblack matrix 52 is comprised of a negative photo-sensitive resist inwhich acrylic pigment is dispersed, or a carbon resist, for instance,has a thickness in the range of 1 to 3 nanometers, has an opticaldensity (OD) of three or higher, and has a sheet resistance of 1×10¹⁰ohms per a unit area.

Then, the red color filter 53R is formed on the substrate 30 through theuse of a negative photo-sensitive resist in which acrylic pigment isdispersed. The red color filter 53R has a thickness in the range ofabout 1.0 to 1.5 micrometers. The blue color filter 53B and the greencolor filter 53G are formed in the same way.

Then, the overcoat layer 54 is formed on the color filters 53R, 53B and53G through the use of novolak resist. The overcoat layer 54 iscomprised of an electrically insulating organic film and has a thicknessin the range of about 2.0 to 3.5 nanometers.

Then, the alignment film 51 composed of polyimide alignment material andhaving a thickness in the range of 30 to 60 nanometers is formed on theovercoat layer 54. Thereafter, a resultant is baked for aligning thealignment film 51. Thus, there is completed the opposing substrate 50.

Then, the TFT substrate 10 and the opposing substrate 50 are aligned toeach other with the above-mentioned sealing material and spacers (notillustrated) being sandwiched therebetween.

Then, liquid crystal 55 composed of fluorine compound is introduced intoa space formed between the substrates 10 and 50, through an inletopening (not illustrated). Then, the inlet opening is closed withsealing material composed of acrylate resin which is hardened whenultra-violet rays are irradiated thereto. Thus, there is obtained aliquid crystal panel having a predetermined gap between the TFTsubstrate 10 and the opposing substrate 50. For instance, a gap may becontrolled by means of a color filter (not illustrated) having pillarsand composed of acrylic resin.

Then, a polarizer 57 comprised of a polarizing film composed of iodinecompound is adhered to a surface of the TFT substrate 10 which surfacedoes not face the opposing substrate 50, and further to a surface of theopposing substrate 50 which surface does not face the TFT substrate 10.

Thus, there is completed a liquid crystal panel including the TFTsubstrate 10 and having a broad viewing angle and a high aperture ratio.

As explained above, in accordance with the first embodiment, it ispossible to accurately and uniformly pattern an indium-tin oxide filminto a pixel electrode by forming an amorphous indium-tin oxide film onan electrically insulating organic film, and baking the amorphousindium-tin oxide film after formation of an alignment film forpoly-crystallizing the amorphous indium-tin oxide film.

In addition, it is possible to reduce an annealing step by one in aprocess of fabricating a TFT substrate.

Second Embodiment

In the second embodiment, plasma is applied onto the electricallyinsulating organic film 33.

The steps in the first embodiment, having been explained with referenceto FIGS. 2 to 11C are carried out. Thus, the electrically insulatingorganic film 33 is now formed on the passivation film 32.

Then, helium (He) plasma is applied all over to a resultant. Applicationof helium plasma is carried out by discharging helium gas at highfrequency in a dry-etching apparatus, for instance.

Thereafter, as illustrated in FIGS. 12 and 13A to 13C, the passivationfilm 32 is etched by photolithography to thereby form the contact hole26 (see FIG. 13A) in alignment with the hole 66, through which thesource electrode 24 is exposed, and a contact hole (not illustrated)through which a metal film of the signal-line terminal 16 is exposed.Concurrently, the passivation film 32 and the gate insulating film 31are etched to form the contact hole 27 (see FIG. 13C) in alignment withthe hole 67, through which the common line 13 is exposed, a contact hole(not illustrated) through which a metal film of the scanning-lineterminal 15 and a metal film of the common-line terminals 18 a and 18 bare exposed, and a contact hole (not illustrated) through which ends ofthe common lines 13 are exposed.

The passivation film 32 and the gate insulating film 31 may be etched bydry etching, wet etching or dry and wet etching.

If the contact hole is formed by dry etching, the substrate is notpost-baked after photoresist has been developed. If the contact hole isformed by wet etching or formed firstly by wet etching and subsequentlyby dry etching, the substrate is post-baked at about 140 degreescentigrade after photoresist has been developed.

Then, as illustrated in FIGS. 2, 3A to 3C and 14 to 16, an electricallyconductive transparent film composed of indium-tin oxide is formed onthe electrically insulating organic film 33 by sputtering, and then, ispatterned by photolithography and etching into the pixel electrode 21,the common electrode 22, the connection electrode 42, the connectionelectrode 82 and the common-line binding lines 17 a and 17 b such that,as illustrated in FIG. 3B, a common electrode 72 among the commonelectrodes 22 is formed on the electrically insulating organic film 33in alignment with the signal line 12, and a pixel electrode 71 among thepixel electrodes 21 is formed on the electrically insulating organicfilm 33 in alignment with the accumulation capacity electrode 35. Thus,the pixel electrode 21 is electrically connected to the source electrode24 through the contact hole 26, the common electrode 22 is electricallyconnected to the common line 13 through the contact hole 27, theconnection electrode 42 is electrically connected to the metal film 41of the scanning-line terminal 15 and common-line terminals 18 a and 18 bthrough the associated contact hole 43, the connection electrode 82 iselectrically connected to the metal film 81 of the scanning-lineterminal 15 through the associated contact hole 83, and the common-linebinding lines 17 a and 17 b are electrically connected to ends of thecommon lines 13 through the contact hole 44.

The indium-tin oxide film is formed in the same condition as that of thefirst embodiment.

The above-mentioned electrically conductive transparent film may becomprised of an indium-zinc oxide (IZO) film in place of an indium-tinoxide (ITO) film. When the electrically conductive transparent film iscomprised of an indium-zinc oxide (IZO) film, a resultant film isamorphous regardless of conditions in which the electrically conductivetransparent film is formed.

A liquid crystal panel including the TFT substrate 10 in accordance withthe second embodiment is fabricated in the same way as the liquidcrystal panel mentioned in the first embodiment.

As explained above, it is possible to accurately and uniformly patternan electrically conductive transparent film such as an indium-tin oxidefilm, and further to prevent increase in a contact resistance betweenthe electrically conductive transparent film and an underlying metalfilm, by applying helium (He) plasma to the electrically insulatingorganic film prior to formation of a contact hole throughout theelectrically insulating inorganic film.

Table 1 shows a relation among film quality of an indium-tin oxide film,line-width shift, and defectiveness in patterning an indium-tin oxidefilm. TABLE 1 Film Quality of ITO Line-width Shift Defectiveness inpatterning Poly-crystal ◯ X Amorphous ◯ ◯◯ (Non-defective)X (Defective)

If an indium-tin oxide film is heated at about 200 degrees centigradeduring being formed or annealed at about 200 degrees centigrade afterformed, a resultant indium-tin oxide film becomes a poly-crystal film.This results in that it would be necessary to lengthen etching time,because an etching rate of an indium-tin oxide film is low, and etchingresidue is likely to be generated. It is possible to controlside-etching of an indium-tin oxide film formed on an electricallyinsulating organic film, to be within about 1 micrometer. No problemsare caused with respect to line-width shift of an indium-tin oxide filmformed on an electrically insulating organic or inorganic film.

However, according to the results of the experiments having beenconducted by the inventors, it was found out there was a problem of acut-out in a patterned indium-tin oxide film formed on an electricallyinsulating organic film. It is considered this is because film qualityof a poly-crystallized indium-tin oxide film is partially non-uniform.

In contrast, an indium-tin oxide film will be amorphous, if theindium-tin oxide film is not heated during formation thereof and/or ifthe indium-tin oxide film is formed in atmosphere containing moisture orhydrogen at about 1 atom %. A resultant indium-tin oxide film would havea high etching rate, and no etching residue would be generated. Etchingtime can be shortened in accordance with an etching rate of anindium-tin oxide film. It is possible to control side-etching of anindium-tin oxide film formed on an electrically insulating organic film,to be within about 1 micrometer. No problems are caused with respect toline-width shift of an indium-tin oxide film formed on an electricallyinsulating organic or inorganic film. It is possible to prevent aproblem of a cut-out in a patterned indium-tin oxide film formed on anelectrically insulating organic film.

Table 2 shows a relation, observed when plasma is applied to anelectrically insulating organic film after formation of a contact hole,among the plasma, uniformity in etching an indium-tin oxide film, and acontact resistance between an indium-tin oxide film and an underlyingmetal film. TABLE 2 Plasma Etching Uniformity Contact Resistance Ar ◯ ◯He ◯ X O₂ — Δ CF₄ X X◯ (Non-defective)X (Defective)— (No Changes)Δ (Not Improved)

Uniformity in etching an indium-tin oxide film is judged based onquality of the common and pixel electrodes in the in-plane switchingtype liquid crystal display device in accordance with the first andsecond embodiments, and further based on non-uniformity in displayedimages, caused by the non-uniformity of etching. A contact resistancebetween an indium-tin oxide film and an underlying metal film is judgedbased on a contact resistance between the indium-tin oxide film and themetal films (chromium films) of the common and signal lines in thein-plane switching type liquid crystal display device in accordance withthe first and second embodiments, and further based on non-uniformity indisplayed images, caused by the contact resistance.

According to the results of the experiments having been conducted by theinventors, the followings are found out.

Application of argon (Ar) plasma ensures quite good uniformity inetching an indium-tin oxide film, and further ensures that a contactresistance is reduced in comparison with no application of argon plasma,if argon plasma is applied in conditions close to conditions selectedfor sputter etching.

Application of helium (He) plasma ensures quite good uniformity inetching an indium-tin oxide film. However, a contact resistance isincreased in comparison with no application of helium plasma. This isconsidered because advantageous effects of sputtering etching are notobtained.

Application of oxygen (O₂) plasma presents etching uniformity equal toetching uniformity obtained when oxygen (O₂) plasma is not applied tothe substrate. That is, no improvement was found. A contact resistanceis slightly improved in comparison with no application of oxygen plasma.Non-uniformity in displayed images, caused by a contact resistance, isnot improved.

Application of fluorine gas plasma such as CF₄ gas deteriorates etchinguniformity and a contact resistance in comparison with no application offluorine gas plasma.

Based on the above-mentioned results, it was found out that heliumplasma should be applied to the substrate prior to formation of acontact hole.

According to the results of the experiments having been conducted by theinventors, it was found out that if an indium-tin oxide film ispost-baked after development of a photoresist in the step of forming acontact hole in the above-mentioned first and second embodiments,uniformity in etching an indium-tin oxide film is deteriorated. Thoughthe reason is not obvious, it is considered that post-baking strengthensclose contact between an electrically insulating organic film and aphotoresist, and hence, since the electrically insulating organic filmis partially removed at its surface when the photoresist is removedafter formation of a contact hole, an exposed surface of theelectrically insulating organic film is influences by remover solution,resulting in poor contact of the electrically insulating organic filmwith a newly formed indium-tin oxide film.

Accordingly, when a contact hole is formed by dry etching, it ispreferable not to post-bake a photoresist.

In contrast, when a contact hole is formed by wet etching or by wet anddry etching, it is necessary to post-bake a photoresist, and hence, itis preferable that helium plasma is applied to the substrate prior toformation of a contact hole. It should be noted that if a contact holeis formed by wet etching, it is necessary to optimize conditions withwhich helium plasma is applied to the substrate and a photoresist ispost-baked, because etchant is likely to penetrate a photoresist due toapplication of helium plasma.

In the above-mentioned first and second embodiments, the interlayerinsulating film 38 is designed to have a multi-layered structurecomprised of the electrically insulating inorganic film 32 and theelectrically insulating organic film 33. It should be noted that theelectrically insulating organic film 33 is formed only on the signalline 12 or only on the signal line 12 and the scanning line 11. That is,the interlayer insulating film 38 is designed to have the multi-layeredstructure including the electrically insulating organic film 33, only inan area extending on the signal line 12 or on the signal and scanninglines 12 and 11, and may be designed to be comprised singly of theelectrically insulating inorganic film 32 in an area except theabove-mentioned area.

The interlayer insulating film 38 in the first embodiment is designed tohave a multi-layered structure comprised of the electrically insulatinginorganic film 32 and the electrically insulating organic film 33. Itshould be noted that the interlayer insulating film 38 in the firstembodiment may be comprised only of the electrically insulating organicfilm 33.

In the above-mentioned first and second embodiments, the commonelectrode 72 is designed to partially cover the signal line 12 therewithexcept an area at which the scanning line 11 and the signal line 12intersect with each other. As an alternative, the common electrode 72may be designed to cover therewith the signal line 12 wholly as well asan area at which the scanning line 11 and the signal line 12 intersectwith each other, or to cover therewith both of the scanning line 11 andthe signal line 12 wholly.

Specifically, the electrically insulating organic film 33 in the firstand second embodiments is used for reducing coupling capacity of thecommon electrode 72 with the signal line 12. Hence, when the commonelectrode 72 is formed to partially cover the signal line 12 therewithexcept an area at which the scanning line 11 and the signal line 12intersect with each other, it is not necessary to form the electricallyinsulating organic film 33 to wholly cover the signal line 12 therewith.The electrically insulating organic film 33 may be formed at least inalignment with the common electrode 72 except an area at which thescanning line 11 and the signal line 12 intersect with each other.

In the first and second embodiments, the present invention is applied toan in-plane switching (IPS) type liquid crystal display device. Itshould be noted that the present invention may be applied to any liquidcrystal display device, if it includes an electrically conductivetransparent film patterned on an electrically insulating organic film.For instance, the present invention may be applied to a twisted nematic(TN) type liquid crystal display device or a vertical alignment (VA)type liquid crystal display device.

In the first and second embodiments, the electrically insulating organicfilm 33 is composed of photo-sensitive novolak resist. As analternative, the electrically insulating organic film 33 may be composedof polyimide resin or acrylic resin.

An electrically insulating organic non-photosensitive film may be usedin place of an electrically insulating organic photosensitive film, inwhich case, steps of etching the film and removing a resist areadditionally carried out.

In the above-mentioned first and second embodiments, the step of forminga contact hole throughout an electrically insulating organic film andthe step of forming a contact hole throughout a passivation film arecarried out under separate photolithography. However, those steps may becarried out under common photolithography.

In the above-mentioned first and second embodiments, the liquid crystaldisplays are designed to include a reverse-stagger channel-etching typethin film transistor. The liquid crystal displays may be designed toinclude a channel-protection type thin film transistor or aforward-stagger type thin film transistor. In addition, the liquidcrystal displays may be designed to include a coplanar type thin filmtransistor in place of a stagger type thin film transistor.

Furthermore, the liquid crystal displays may be designed to include apolysilicon (p-Si) thin film transistor in place of an amorphous (a-Si)silicon thin film transistor.

The liquid crystal displays may be designed to include ametal-insulator-metal (MIM) as a switching device in place of a thinfilm transistor.

While the present invention has been described in connection withcertain preferred embodiments, it is to be understood that the subjectmatter encompassed by way of the present invention is not to be limitedto those specific embodiments. On the contrary, it is intended for thesubject matter of the invention to include all alternatives,modifications and equivalents as can be included within the spirit andscope of the following claims.

The entire disclosure of Japanese Patent Applications Nos. 2002-311526and 2003-362206 filed on Oct. 25, 2002 and Oct. 22, 2003, respectively,including specification, claims, drawings and summary is incorporatedherein by reference in its entirety.

1. A method of fabricating a liquid crystal display device, comprisingthe steps of: (a) fabricating a switching device on a substrate; (b)forming an interlayer insulating film on said substrate such that saidswitching device is covered with said interlayer insulating film, saidinterlayer insulating film being comprised of an electrically insulatinginorganic film and an electrically insulating organic film formed onsaid electrically insulating inorganic film; and (c) forming atransparent electrode on said interlayer insulating film, saidtransparent electrode being electrically connected to said switchingdevice through said interlayer insulating film, said step (c) including:(c1) patterning said electrically insulating organic film; (c2) forminga contact hole throughout said electrically insulating inorganic film;(c3) depositing electrically conductive transparent material on saidinterlayer insulating film; and (c4) patterning said material into saidtransparent electrode, said step (c2) including: (c2-1) forming aphotoresist on said interlayer insulating film in a predeterminedpattern; and (c2-2) applying dry-etching to said electrically insulatinginorganic film with said photoresist being used as a mask withoutpost-baking said photoresist.
 2. The method as set forth in claim 1,wherein said electrically insulating organic film is formed coveringtherewith at least partially at least a signal line including a drainelectrode of said switching device, in said step (c1).
 3. The method asset forth in claim 1, wherein said step (a) includes the steps of: (a1)forming both a scanning line including a gate electrode of saidswitching device and a common line through which a common voltage isapplied, on said substrate; (a2) forming a gate insulating film on saidsubstrate such that said scanning line and said common line are coveredwith said gate insulating film; (a3) forming a semiconductor layer onsaid gate insulating film, said semiconductor layer acting as an activelayer of said switching device; and (a4) forming both a signal lineincluding a drain electrode of said switching device and a sourceelectrode of said switching device, said signal line intersecting withsaid scanning line, and said step (c5) including the step of patterningsaid electrically conductive transparent material into a pixel electrodeand a common electrode on said interlayer insulating film, said pixelelectrode being in electrical connection with said switching device,said common electrode being in electrical connection with said commonline.
 4. The method as set forth in claim 1, wherein said electricallyconductive transparent material is indium-tin oxide (ITO) or indium-zincoxide (IZO).